Natural rubber characterization

Chattopadhyay S., Chaki T.K., and Bhowmick A.K., New thermoplastic elastomers from poly(ethyle-neoctene) (engage), poly(ethylene-vinyl acetate) and low-density polyethylene by electron beam technology structural characterization and mechanical properties. Rubber Chem. TechnoL, 74, 815, 2001. Roy Choudhury N. and Dutta N.K., Thermoplastic elastomeric natural rubber-polypropylene blends with reference to interaction between the components. Advances in Polymer Blends and Alloys Technology, Vol. 5 (K. Finlayson, ed.), Technomic Publishers, Pensylvania, 1994, 161. 

From a theoretical point of view, the equilibrium modulus very probably gives the best characterization of a cured rubber. This is due to the relationship between this macroscopic quantity and the molecular structure of the network. Therefore, the determination of the equilibrium modulus has been the subject of many investigations (e.g. 1-9). For just a few specific rubbers, the determination of the equilibrium modulus is relatively easy. The best example is provided by polydimethylsiloxane vulcanizates, which exhibit practically no prolonged relaxations (8, 9). However, the networks of most synthetic rubbers, including natural rubber, usually show very persistent relaxations which impede a close approach to the equilibrium condition (1-8). 

Butyl rubber is produced by a process in which isobutylene is copolymerized with a small amount of isoprene using aluminum chloride catalyst at temperatures around — 150° F. (20). The isoprene is used to provide some unsaturation, yielding a product that can be vulcanized (43). Vulcanized Butyl rubber is characterized by high tensile strength and excellent flex resistance furthermore, as a result of its low residual unsaturation (only 1 to 2% of that of natural rubber) it has outstanding resistance to oxidative aging and low air permeability. These properties combine to make it an ideal material for automobile inner tubes (3), and Butyl rubber has continued to be preferred over natural rubber for this application, even when the latter has been available in adequate supply. 

The tensile curves are characterized by a sharp decrease in tensile with loading at low loadings. For rayon, acrylic, and fiber glass the tensile was minimized at approximately 20 volumes. For nylon the minimum was reached at approximately 50 volumes. Beyond the minimum points in the curves the tensile increased but at a slower rate than the initial rate of decrease. Eventually the tensile reached that of the natural rubber matrix for all but the nylon fibers. Since the loading resulting in... 

About 40 different grades of regular butyl rubbers are available [63], depending on molar mass (Afv 3-6-105, polydispersity MW M 3-5) and on unsaturation level. For 0.7 mol% of isoprene the molar mass of subchain in the cross-linked rubber is =8000, and =2500 for the highest level (2.2%), which is much more than in polydienes or natural rubber networks. They are shared in two main families characterized by their range of Mooney viscosity, typically ML(I + 8)(100°C) 41-57 and 60-80. 

Sando, T., Takaoka, C., Mukai, Y., Yamashita, A., Hattori, M., Ogasawara, N., Fukusaki, E. and Kobayashi, A. (2008) Cloning and characterization of meval-onate pathway genes in a natural rubber producing plant, Hevea brasiliensis. Biosci. Biotechnol. Biochem., 71, 2049-60. 

The usefulness of analytical pyrolysis in polymer characterization, identification, or quantitation has long been demonstrated. The first application of analytical pyrolysis can be considered the discovery in 1860 of the structure of natural rubber as being polyisoprene [10]. This was done by the identification of isoprene as the main pyrolysis product of rubber. Natural organic polymers and their composite materials such as wood, peat, soils, bacteria, animal cells, etc. are good candidates for analysis using a pyrolytic step. 

Moore, C.G. Trego, B.R. Structural characterization of vulcanizates. Part IV. Use of triphenylpho-sphine and sodium di-n-butyl phosphite to determine the structures of sulfur linkages in natural rubber, cis-l,4-polyisoprene, and ethylene-propylene rubber vulcanizate networks. J. Appl. Polym. Sci. 1964, 8, 1957. 

Campbell, D.S. Structural characterization of vulcanizates part X. Thiol-disulfide interchange for cleaving disulfide crosslinks in natural rubber vulcanizates. Rubber Chem. Technol. 1970,43,210. 

According to this mechanism, natural rubber chains are expected to have one dimethylallyl terminal unit and one isoprenyl pyrophosphate terminal unit the latter may give rise to a hydroxyl group by hydrolysis. From this point of view, acyclic terpenes in the generalized structure (II) may be appropriate models for the structural characterization of natural polyisoprenes by 13C NMR spectroscopy. 

Ceresa, R. J. "Synthesis and Characterization of Natural Rubber Block"and "Graft Copolymers in Block and Graft Copolymerization" Ceresa, R. J., Ed. John Wiley New York, 1973 Chap, 3. 

R.J.Ceresa, "Syntheses and Characterization of Natural Rubber Block and Graft Copolymers", in R.J. Ceresa ed.. Block and Graft Copolymerization, Volume 1, John Wiley, London, Chapter 3, 1973. 

Our analytical procedure consists of stepwise acetone extraction followed by cyclohexane. Subsequently, the acetone-soluble fraction is partioned between hexane/aqueous ethanol (12,15), and the soluble components are freed of solvents and determined gravimetrically. For lack of specific nomenclature, the botanochemicals isolated by this technique have been referred to as "whole plant oil," "polyphenol," and "polymeric hydrocarbon." Actually, components from these extracts need to be further characterized. However, petroleum refinery processes may be sufficiently insensitive to allow use of carbon-hydrogen rich compounds represented by a broad spectrum of structures. For example, consider the diverse chemicals ranging from methanol to natural rubber which have been converted to gasoline (16). Thus, chemical species may be important if chemical intermediates are being generated but may be nonconsequential for production of fuels, solvents, carbon black, and other basic chemicals. 

Building on technologies first developed in Germany in the early 1930s, Robert M. Thomas and William J. Sparks, both employees of Standard Oil (now ExxonMobil Chemical), patented a new synthetic rubber in 1937. Butyl rubber is characterized by a very saturated linear polymer chain, leaving little space between molecules for transmission of air, vapors, moisture, or water. As such, butyl rubber was successfully used during World War II as a substitute for natural rubber in the manufacture of tire inner tubes and curing bladders. 

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